Managing rising mine water to

prevent aquifer pollution

Dr Ian Watson

The Coal Authority

East of Wear Mining Block

Horden

Dawdon

Easington

Minewater flow

Minewater flow

River

Wear

2002: Rising Minewater Levels

Water Level Projections for Sites East of Wear

0

50

100

150

200

250

300

350

400

450

Jun-94 Jun-95 Jun-96 Jun-97 Jun-98 Jun-99 Jun-00 Jun-01 Jun-02 Jun-03 Jun-04 Jun-05 Jun-06 Jun-07 Jun-08 Jun-09 Jun-10

Date

Wate

r L

evel

(mB

GL

)

-387

-337

-287

-237

-187

-137

-87

-37

13

63

Wate

r L

evel

(mA

OD

)

Horden (2) Horden Projected Water Level Ordnance Datum Line

Sea Level

Projection

showing impacts

starting from

2004

26 May 2011 4

The Pollution Threat in East Durham

Deep Coastal

Shaft

Colliery Beach

Adit

River Wear Inland

Permian Magnesian Limestone Aquifer

Carboniferous Coal Measures

North Sea

26 May 2011 5

Key Contaminants

Predictions made from :

Water quality during mining

Samples from shafts during rebound

Iron - up to 200 mg/l

Salinity - Hypersaline

Chlorides - 20,000 to 30,000 mg/l

Sulphate – 3,000 to 5,000 mg/l

26 May 2011 6

Source Protection Zones

Horden

Dawdon

Permian Magnesian

Limestone Aquifer

c. 36 Million Litres /

day abstracted by

Northumbrian Water

Ltd:

150,000 people rely

on this major aquifer

for drinking water

26 May 2011 7

Possible Impacts

Coastal

Pollution

Aquifer

Pollution River

Pollution

Horden Control of Water Levels

Water Levels for East of Wear - Coastal

-130

-110

-90

-70

-50

-30

-10

10

Jan-00 Jan-01 Jan-02 Jan-03 Jan-04 Jan-05 Jan-06 Jan-07 Jan-08

Date

Wate

r L

evel (m

AO

D)

Daw don Easington Horden Haw thorn

Pumping commenced August 2004

Horden Temporary Active Treatment Scheme

Horden Temporary Active Treatment Scheme

Horden Shaft Water Profile

Salinity and Iron

increase with

pumpingDEPTH DOWN SHAFT

Salinity and Iron

increase with

Depth

Horden Pumped Water Quality

Salinity and Iron

increase as

pumping increase

from c50 l/s to

c100 l/s

Hydraulic Control Risks

Horden

Dawdon

Easington

Minewater flow

Minewater flow

?

River

Wear

Single Roadway Connection

- Recorded as dammed

- Currently flowing freely

- Could become restricted or blocked

- Horden would not be able to control

the whole area.

26 May 2011 14

Proposed Two Site Strategy

Main pump/treat site at DawdonFor hydraulic control North of Ludworth Dyke

Dawdon shaft is deeper than Horden

Expect worse quality mine water

Higher chlorides, iron etc.

Active treatment technology to remove Iron

150 l/s capacity

Secondary pump/treat site at HordenExisting 100 to 150 l/s capacity temporary active plant

Chlorides high due to high pumping rate

Reduce to 50 l/s when Dawdon on stream

If chlorides reduce replace with passive plant

Settling lagoons and reed beds

26 May 2011 15

Twin Sea Outfalls

Transfer Pipelines

Treatment Plant

Existing Shaft (Pumps & Controls)

Cross section of sea outfall

26 May 2011 16

Treatment Layout

Blower RoomTransformers,

Panels and

Control Room Workshop/lab

Lime

Silo

Sludge Thickening and

Disposal

(Filter-press)Clarifier Clarifier Clarifier

Stage 2

Reactor

Stage 2

Reactor

Stage 2

Reactor

Sludge

Holding

Tank

Stage 1

ReactorStage 1

ReactorStage 1

Reactor

Sludge

Holding

Tank

De-

Gassing

Tank

De-

Gassing

Tank

De-

Gassing

Tank

Polymer

Make-up Area

Mixed Lime

Holding

Tank

Lime Mixing Tanks

Outlet

Tank

Process

water

stock

1 2 3

26 May 2011 17

Process Construction

Multi disciplinary project

Over 30 different sub-contractors

Complex programming

26 May 2011 18

Short Sea Outfall

Coastal Modelling:

Dispersion Modelling and Sea Bed Survey

Directional Drilling - from cliff top to sea bed

26 May 2011 19

Pumping at Dawdon

Dawdon

Starts

pumping

Control

throughout

coalfield

confirmed

26 May 2011 20

Status in 2008

Preventing Aquifer Pollution by:

2 Active Pump & Treat schemes:

Horden Temporary

Dawdon

Final Phase:

Replace Horden active with Passive

New Lagoons and reedbeds

Reedbeds depend on decreased Chloride

26 May 2011 21

Horden Quality 2004-2010

Salinity and Iron

peaked and

decreased, as

pumping

decreased from

c100 l/s to c50 l/s

26 May 2011 22

Shaft &

Cascade

Outlet Point

Settlement

Lagoons

Reedbeds

26 May 2011 23

Horden/Dawdon Timetable

June 2004 Horden active plant operational

Nov 2008 Dawdon active plant operational 150 l/s

Reduce Horden rate to ~50 l/s

2010 Commence construction of Horden passive plant

2011 Horden passive plant operational

Dismantle Horden active plant

26 May 2011 24

Horden Passive

forming of lagoon cells

26 May 2011 25

Horden Passive

- Lining the cells

26 May 2011 26

Aerial View May 2011

Treatment Area = 1.7 ha

26 May 2011 27

Morlais, South Wales

at commissioning

26 May 2011 28

Summary

Pumping at 2 sites

Dawdon Active treatment for:

High flows of poor quality water

Horden Passive treatment for:

Smaller flows of better quality water

Drinking Water Aquifer protected